The biomass is a renewable resource and plays a role in preventing global warming by inhibiting the emission of carbon dioxide. Processes of converting the biomass to ethanol, lactic acid, and other useful chemical products by an enzymatic or chemical method are being examined in the production of chemical products from the biomass (biorefinery). Currently, starch derived from corn is the main material employed in biorefinery. In terms of the quantity of resources of primary structural components of plants that are available, cellulose is present in overwhelmingly greater quantity than starch. However, the techniques to convert cellulose to chemically useful products by reducing the molecular weight thereof has not been developed, and this resource is currently virtually untapped. (See Koshijima et al., Functional Cellulose, CMC Publishing Co., Ltd. (2003), and The Japan Institute of Energy, ed., Biomass Handbook, Ohmsha (2002), the entire contents of which are hereby incorporated by reference herein.) For example, a large number of research has been conducted into degrading cellulose with enzymes. However, major problems remain with enzymatic methods because of low reaction rates and the need to greatly enhance activity and separate the enzyme from the product. Processes of obtaining glucose by hydrolysis with sulfuric acid or hydrofluoric acid have been attempted in the degradation of cellulose with catalysts. However, such processes have not been put into general practice due to corrosion of reactors with an acid, hazards, and the production of large amounts of neutralization waste becoming a major load on the environment.
In precedent researches of the chemical conversion of cellulose with catalysts, Balandin and Vasyunina, et al., have conducted hydrogenation with a supported ruthenium catalyst to produce sorbitol from sulfite cellulose with a yield of 82 percent (see A. A. Balandin, N. A. Vasyunina, G. S. Barysheva, S. V. Chepigo, Izv. Akad. Nauk SSSR, Ser. Khim., 392 (1957), the entire contents of which are hereby incorporated by reference herein.). However, there is no description of the use of cellulose itself as a raw material. Further, in this reaction, the use of sulfuric acid requires separation of the product, and presents problems in the form of the generation of neutralization waste and the corrosion of reactors. The same group employed silk cellulose that had been treated with alkali and acid as a raw material, and conducted hydrogenation with supported Raney nickel in the presence of nickel sulfate in an aqueous solution to obtain sorbitol (see N. A. Vasyunina, A. A. Balandin, G. S. Barysheva, S. V. Chepigo, Yu. L. Pogpsov, Z. Prik. Khim., 37, 2725 (1964), the entire contents of which are hereby incorporated by reference herein). Here again, the cellulose has to be pretreated and the product separation is not easy. Specht et al. used a mixture of cellulose and hemicellulose that had been treated by hydrolysis as a raw material, and after adjustment of its pH at 8 or greater, sugar alcohols was synthesized by hydrogenation with supported Raney nickel catalyst (see H. Specht and H. Dewein, DE 1066567 (1959), the entire contents of which are hereby incorporated by reference herein). However, cellulose pretreatment and pH adjustment were required.
Although cellulose is insoluble in water, most starches with similar structure are water soluble. Since hydrolysis and hydrogenation reactions of water-soluble starch proceed smoothly, a large number of research has been conducted in this area. Atlas Powder Corp. employed a Ni/diatomaceous earth catalyst to hydrogenate starch and obtain polyols (see Atlas Powder, GB 872809 (1961), the entire contents of which are hereby incorporated by reference herein).
Kruse et al. employed a Ru/USY catalyst to synthesize sorbitol from cornstarch in two-steps (see W. M. Kruse and L. W. Wright, U.S. Pat. No. 3,963,788 (1976), the entire contents of which are hereby incorporated by reference herein).
Jacobs et al. employed a Ru/USY catalyst to synthesize sorbitol in a single step (see P. Jacobs and H. Hinnekens, EP 0329923 (1989), Japanese Unexamined Patent Publication (KOKAI) Heisei No. 1-268653, or English family member EP 0329923A1; the entire contents of which are hereby incorporated by reference herein). Hydrogenation of water-insoluble cellulose is not conducted in the cited references. Moreover, the catalysts are limited to high-dispersion ones with a Ru dispersion of 0.58 or higher.
As shown above, in the conventional production of sugar alcohols, such as sorbitol, by the hydrolysis and hydrogenation of cellulose, the cellulose is always treated with an acid or an alkali to increase solubility in water, and then employed as a reaction substrate; there is no example of water-insoluble cellulose itself being used. Further, the need to separate the catalyst and product, adjust the pH, neutralize the acid or alkali, and activate the catalyst during reuse create problems in the form of a major load on the environment.
Accordingly, the objects of the present invention are to provide a catalyst for use in the production of sugar alcohols by the hydrolysis and hydrogenation of cellulose that permits the use of cellulose without pretreatment, that affords easy separation of catalyst and product, and that does not require pH adjustment, acid or alkali neutralization, or activation of the catalyst during reuse, and to provide a method for producing sugar alcohols from cellulose employing this catalyst.